1. Technical Field of the Invention
The present invention relates to a magnetoresistive effect element for reading the magnetic field intensity of a magnetic recording medium etc. as signals, a thin film magnetic head comprising the element, and a head gimbal assembly and magnetic disk device including the thin film magnetic head.
2. Description of the Related Art
As the surface recording density of a magnetic disk device has lately been increasing, there is a need for enhancing a performance of a thin film magnetic head. As a thin film magnetic head, a complex type thin film magnetic head has widely been used that has a laminated structure of a reproducing head having a read-only magnetoresistive effect element (hereafter also referred to as an MR element) and a recording head having a write-only induction type magnetism conversion element.
Examples of the MR element include anisotropic magnetoresistive effect (AMR) elements utilizing an anisotropic magnetoresistive effect, giant magnetoresistive effect (GMR) elements utilizing a giant magnetoresistive effect, and tunnel type magneto resistive effect (TMR) elements utilizing a tunnel type magneto resistive effect.
The reproducing head is particularly required to be highly sensitive and yield high output. As reproducing heads satisfying such requirements, GMR heads using the spin valve type GMR element have already been in mass production. Recently, the reproducing head using the TMR element has also been in mass production in accordance with further increased surface recording densities.
The spin valve type GMR element generally has a nonmagnetic intermediate layer, a free layer formed on one surface of the nonmagnetic intermediate layer, a magnetic pinned layer formed on the other surface of the nonmagnetic intermediate layer, and a pinning layer (generally an antiferromagnetic layer) formed in contact with the magnetic pinned layer on the opposite side thereof to the nonmagnetic intermediate layer. The free layer is a layer of which the magnetization direction changes in accordance with the signal magnetic field from an external source. The magnetic pinned layer is a layer of which the magnetization direction is pinned by the exchange-coupling magnetic field from the pinning layer (antiferromagnetic layer).
The majority of traditional GMR heads have a CIP-GMR element having the CIP (current in plane) structure in which the magnetic signal detection current (so-called sense current) is applied in parallel to the planes of the layers composing the GMR element, and such an element has been in mass production.
On the other hand, a GMR element having the CPP (current perpendicular to plane) structure (the CPP-GMR element) in which the sense current is applied perpendicular to the planes of the layers composing the GMR element (in the lamination direction) has been developed as a next generation element, and an attempt has been made to mass produce the TMR element, which is a type of CPP-GMR element.
The TMR element generally has a free layer, a magnetic pinned layer, a tunnel barrier layer (nonmagnetic intermediate layer) interposed between them, and an antiferromagnetic layer provided on the opposite surface of the magnetic pinned layer to the surface in contact with the tunnel barrier layer. The tunnel barrier layer is a nonmagnetic insulating layer that allows electrons to pass through with their spin maintained by the tunnel effect. Other layers such as the free, magnetic pinned, and antiferromagnetic layers are basically the same as those used in the spin valve type GMR element.
Both the TMR element, which is now in mass production, and the CPP-GMR element, which is under development, must have narrower tracks and read gaps for realizing further increased recording densities.
The typical spin valve type CPP-GMR element including aforementioned TMR element is structured as a laminated body primarily consisting, from the bottom in consideration of the lamination order, of a lower electrode, an antiferromagnetic layer, a first ferromagnetic layer (magnetic pinned layer), a nonmagnetic intermediate layer, a second ferromagnetic layer (free layer), and an upper electrode. The magnetization direction of the first magnetic layer, which is one of the ferromagnetic layers, is pinned perpendicularly to the magnetization direction of the second ferromagnetic layer when the externally applied magnetic field is zero. The magnetization direction of the first ferromagnetic layer can be pinned by placing an antiferromagnetic layer next to the first ferromagnetic layer so as to cause exchange-coupling, by which unidirectional anisotropic energy (also referred to as exchange bias or coupled magnetic field) is provided to the first ferromagnetic layer. Therefore, the first ferromagnetic layer is also called a magnetic pinned layer, as referred to above, or a pinned layer. Such an element has a larger resistance value and is subject to larger fluctuation in resistance as it has a smaller cross-sectional area. In other words, the element has a structure suitable for reduced track width or narrower tracks.
The thin film magnetic head having the above spin valve type CPP-GMR element is provided with bias magnetic field application layers on two sides of an MR element. The bias magnetic field application layers apply a so-called vertical bias to the element. Consequently, the second ferromagnetic layer serving as a free layer has a single domain, preventing occurrence of noise and allowing for detection of a specific external magnetic field.
However, the traditional magnetoresistive effect element has an antiferromagnetic layer within the region serving as an MR sensor as understood from the above described MR laminated film structure. There is the problem that, as the tracks narrow, the probability of pin reversal of the magnetic pinned layer (hereafter simply termed “pin reversal”) is increased. This results from the grain size of the antiferromagnetic layer being non-negligibly small in relation to the track width. The antiferromagnetic layer generally has a grain size of approximately 20 nm. The track width required in the next generation recording density class of 500 Gbpsi is approximately 50 nm. Then, the number of grains in the antiferromagnetic layer in the track width direction is anticipated to be 2 to 3 (50 nm divided by 20 nm).
In this way, reduction in the number of grains composing the antiferromagnetic layer causes weakened exchange-coupling between the antiferromagnetic layer and first ferromagnetic layer and variation in magnetic properties. Therefore, the pin reversal problem may easily occur during so-called wafer process and lapping process. The pin reversal problem presumably becomes a more serious problem as recording density is further increased.
Furthermore, since the antiferromagnetic layer is provided in the region serving as the MR sensor, it is difficult to comply with demand for the narrower read gaps (reduced distance between upper and lower shield layers) required for higher recording densities.
In the above circumstances, the invention of the present application is proposed, the purpose of which invention is to provide a magnetoresistive effect element in which the antiferromagnetic layer provided between the upper and lower shields is eliminated and the antiferromagnetic layer is provided in a so-called shield layer so as to resolve the above pin reversal problem and allow for much narrower read gaps.